1. Field of the Invention
The present invention relates to a method and apparatus for inputting information including coordinate data. More particularly, the present invention relates to a method and apparatus for inputting information including coordinate data of a location of a coordinate input member, such as a pen, a human finger, etc., on an image displayed on a relatively large screen.
2. Discussion of the Background
Lately, presentation systems, electronic copy boards, or electronic blackboard systems provided with a relatively large screen display device, such as a plasma display panel, a rear projection display, etc., are coming into wide use. Certain type of presentation systems also provide a touch input device disposed in front of a screen for inputting information related to the image displayed on the screen. Such a touch input device is also referred as an electronic tablet, an electronic pen, etc.
As to such a presentation system, for example, when a user of the system touches an icon on a display screen, a touch input device detects and inputs the touching motion and the coordinates of the touched location. Similarly, when the user draws a line, the touch input device repetitively detects and inputs a plurality of coordinates as a locus of the drawn line.
As an example, Japanese Laid-Open Patent Publication No. 11-85376 describes a touch input apparatus provided with light reflecting devices disposed around a display screen, light beam scanning devices, and light detectors. The light reflecting device has a characteristic to reflect incident light toward a direction close to the incident light. During an operation of the apparatus, scanning light beams emitted by the light beam scanning devices are reflected by the light reflecting devices, and then received by the light detectors. When a coordinate input member, such as a pen, a user's finger, etc., touches the surface of the screen at a location, the coordinate input member interrupts the path of the scanning light beams, and thereby the light detector is able to detect the touched location as a missing of the scanning light beams at the touched location.
In this apparatus, when a certain location-detecting accuracy in a direction perpendicular to the screen is required, the scanning light beams are desired to be thin and to scan on a plane close enough to the screen. Meanwhile, when the surface of the screen is contorted, the contorted surface may interfere with the transmission of the scanning light beams, and consequently a coordinate input operation might be impaired. As a result, for example, a double-click operation might not be properly detected, free hand drawing lines and characters might be erroneously detected, and so forth.
As another example, Japanese Laid-Open Patent Publication No. 61-196317 describes a touch input apparatus provided with a plurality of television cameras. In the apparatus, the plurality of television cameras detect three-dimensional coordinates of a moving object, such as a pen, as a coordinate input member. Because the apparatus detects a three-dimensional coordinates, the plurality of television cameras are desirable to capture images of the moving object at a relatively high flame rate.
As further example, a touch input apparatus provided with an electro magnetic tablet and an electromagnetic stylus is known. In this apparatus, a location of the stylus is detected based on electromagnetic induction between the tablet and the stylus. Therefore, a distance between the tablet and the stylus tends to be limited in a rather short distance, for example, eight millimeters; otherwise a large size stylus or a battery powered stylus is used.